Are inner classes commonly used in Java? Are they “bad”? [closed]

Answer 1

They are useful and can be very commonly used. While you should be cautious about abusing the functionality, they aren't much more liable to be abused than any other language feature.

Answer 2

A good example of an inner class is the iterator implementation for a given collection type. Its a class that implements a public interface, but has no business existing except in association with another class. It allows you to model things that in C++ you would be forced to do with the friend operator.